Ubuntu 20.04
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Docker : Use Persistent Storage
2020/06/02
 
When Container is removed, data in it are also lost, so it's necessary to use external filesystem in Container as persistent storage if you need.
[1] For exmaple, create a Container only for using to save data as a storage server with an image busybox.
root@dlp:~#
vi Dockerfile
# create new

FROM busybox
MAINTAINER ServerWorld <admin@srv.world>

VOLUME /storage
CMD /bin/sh

# build image

root@dlp:~#
docker build -t storage ./
root@dlp:~#
docker images

REPOSITORY               TAG                 IMAGE ID            CREATED             SIZE
storage                  latest              4b03c60b9191        1 second ago        1.22MB
nginx_server             latest              2d5672bca343        9 minutes ago       155MB
srv.world/ubuntu_nginx   latest              d30733d4f315        2 hours ago         155MB
busybox                  latest              78096d0a5478        2 weeks ago         1.22MB
ubuntu                   latest              1d622ef86b13        5 weeks ago         73.9MB

# generate a Container with any name you like

root@dlp:~#
docker run -it --name storage_server storage

/ #
exit
[2] To use the Container above as a Storage Server from other Containers, add an option [--volumes-from].
root@dlp:~#
docker run -it --name ubuntu_server --volumes-from storage_server ubuntu /bin/bash
root@58f8259662f7:/#
df -hT

Filesystem                        Type     Size  Used Avail Use% Mounted on
overlay                           overlay   77G  3.2G   71G   5% /
tmpfs                             tmpfs     64M     0   64M   0% /dev
tmpfs                             tmpfs    5.9G     0  5.9G   0% /sys/fs/cgroup
shm                               tmpfs     64M     0   64M   0% /dev/shm
/dev/mapper/ubuntu--vg-ubuntu--lv ext4      77G  3.2G   71G   5% /storage
tmpfs                             tmpfs    5.9G     0  5.9G   0% /proc/acpi
tmpfs                             tmpfs    5.9G     0  5.9G   0% /proc/scsi
tmpfs                             tmpfs    5.9G     0  5.9G   0% /sys/firmware

root@58f8259662f7:/#
echo "persistent storage" >> /storage/testfile.txt

root@58f8259662f7:/#
ls -l /storage

total 4
-rw-r--r-- 1 root root 19 Jun  2 07:00 testfile.txt
[3] Make sure datas are saved to run a Container of Storage Server like follows.
root@dlp:~#
docker start storage_server

storage_server
root@dlp:~#
docker exec -it storage_server cat /storage/testfile.txt

persistent storage
[4] For other way to save data in external filesystem, it's possible to mount a directory on Docker Host into Containers.
# create a directory

root@dlp:~#
mkdir -p /var/lib/docker/disk01

root@dlp:~#
echo "persistent storage" >> /var/lib/docker/disk01/testfile.txt
# run a Container with mounting the directory above on /mnt

root@dlp:~#
docker run -it -v /var/lib/docker/disk01:/mnt ubuntu /bin/bash
root@dafa8f40e41a:/#
df -hT

Filesystem                        Type     Size  Used Avail Use% Mounted on
overlay                           overlay   77G  3.2G   71G   5% /
tmpfs                             tmpfs     64M     0   64M   0% /dev
tmpfs                             tmpfs    5.9G     0  5.9G   0% /sys/fs/cgroup
shm                               tmpfs     64M     0   64M   0% /dev/shm
/dev/mapper/ubuntu--vg-ubuntu--lv ext4      77G  3.2G   71G   5% /mnt
tmpfs                             tmpfs    5.9G     0  5.9G   0% /proc/acpi
tmpfs                             tmpfs    5.9G     0  5.9G   0% /proc/scsi
tmpfs                             tmpfs    5.9G     0  5.9G   0% /sys/firmware

root@dafa8f40e41a:/#
cat /mnt/testfile.txt

persistent storage
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